A locking device of this type comprising two safety elements and an electrical query device is disclosed in DE 10 2004 056 086 B3. A spring which may come to bear against one of the safety elements serves as a transducer for a micro-switch.
US 2008/093875 A1 discloses a locking device for a vehicle seat having a housing, a pawl mounted in a movable manner on the housing for locking with a mating element, at least one safety element which is provided for securing the pawl in the locked state, and can be moved relative to the pawl for unlocking the device, and a query device which queries the locked state of the locking device, and has a transducer and a sensor, the query device being designed in a contactless manner, and the transducer and the sensor interacting with each other due to the relative positioning and/or movement thereof. Moreover, at a different point a second mechanical query device is provided with a further transducer and sensor.